| Nowadays, the problems of environment and energy become more and moreprominent, the development of clean and renewable energy resources has become animportant strategy for sustainable economic and social development. The micro-grid hasbeen paid more and more attention all over the world for it can reduce the feeder loss,increase local power supply reliability and improve the efficiency of energy use. However,the access of micro-grid with a number of distributed generation（DG） and energy storagewill change the characteristics of the distribution system failure. The change of current afterfault will become very complex and may cause the traditional protection can’t judgelocation of the fault accurately. So the reconfiguration of distribution system protection isthe key of micro-grid applications.The micro-grid consists of distributed generation, load, energy storage devices andcontrol device. It can work in both grid-connected and grid-isolated mode. First, this paperanalyzes the control mode of micro-grid and the control mode of DG inverter ingrid-connected and grid-isolated operation mode. Each DG inverter in micro-grid generallyadopts the P/Q control mode in grid-connected mode. When it’s in grid-isolated mode, oneor a few DGs are needed to adopt U/f and Droop control strategy for micro-grid mustmaintain the ratings of voltage and frequency. Then the equivalent model of inverter DG ingrid-connected mode is established. The simulation model of distribution system withmicro-grid in PSCAD/EMTDC is established based on the analysis of distribution networkstructure and protection configuration. Then on the basis of the analysis of DG faultcharacteristics, the effect of micro-grid on the conventional relay protection of distributionnetwork is analyzed in detail, including the protection maloperation, refusing to operate, thedecrease of sensitivity and the effects of reclosure etc.. Finally, a scheme of relay protectionbased on communication considering the reclosing device is proposed. At last，use thesimulation model in PSCAD/EMTDC to validate the new scheme of the relay protection. |
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